@remy/pstree/lib/index.js

Collects the full tree of processes from /proc

const exec = require('child_process').exec;
const psTree = require('ps-tree');
const utils = require('./utils');
var hasPS = true;

// discover if the OS has `ps`, and therefore can use psTree
exec('ps', error => {
  module.exports.hasPS = hasPS = !error;
});

module.exports = function main(pid, callback) {
  if (typeof pid === 'number') {
    pid = pid.toString();
  }

  if (hasPS && !process.env.NO_PS) {
    return psTree(pid, callback);
  }

  utils
    .getStat()
    .then(utils.tree)
    .then(tree => utils.pidsForTree(tree, pid))
    .then(res => callback(null, res))
    .catch(error => callback(error));
};

module.exports.hasPS = hasPS;